Smartphones and tablet computers become increasingly popular. Using a tablet computer for learning and entertainment on public transportation vehicles such as a subway and a bus has become a trend. However, as a frame of the tablet computer is getting narrower, it is prone to cause a misoperation when the tablet computer is held by hand. When a subway or a bus starts and stops, there is quite large inertia, and people cannot hold onto a handrail when operating a tablet computer with both hands, which causes a quite high potential risk to physical safety. Moreover, it is difficult to hold the tablet computer with one hand.